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| Where might these snails live? |
How about this small fern? |
Where would you find this print? | Does this look familiar? |
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To Be fossilized, Organisms Have to Be:
Pseudofossils: Look Like Fossils But Aren't
Fossil or Fake? What do you think about these few examples?
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Major Understandings:
1.2j Geologic history can be reconstructed by observing sequences of rock types and fossils to correlate bedrock at various locations.
The Geologic Time Table: page 8 and 9 reference tables.
Watch this quicktime movie to see what creatures lived in each period!
PDF Timeline by Charles Burrows
Activity: Using your reference tables (word)
Answer these questions according to your Reference Tables.
1. How many Eras make up the Phanerozoic Eon?
2. How many years ago did the Cambrian period begin?
3. How old is the Earth?
4. How long has the Northeastern continental margin been passive?
5. What is the name of the oldest index fossil found in New York?
6. Which lasted longer the Paleozoic or the Proterozoic?
7. Between what two periods did the dinosaurs become extinct?
8. During what period did the Acadian Mountains form in New York?
9. Which lived for a longer period of time the dinosaurs or mammals?
10. How long have humans existed on the earth?
What geologic period could these fossils have lived?
| New York State Fossil | Ammonites | Trilobites | Tyrannosaurus Rex |
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Extinction!
Geologic Eras are separated by drastic changes in the evolutionary record.
Explore the K-T Boundary
Evidence for the extinction of dinosaurs by impact:
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Forams before
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Forams After
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K-T Clay layer
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Iridium levels
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Our Earth's Largest Extinction was not the extinction of the dinosaurs!
Relative Time:
Absolute Time:
Finding age with relative time
Activities
Guidelines for figuring out a sequence:
Law of Superposition: oldest rock layer on the bottom and the layers get younger as you move up.
Law of Original Horizontality- Rocks are deposited flat and level because they are deposited in deep water placing the oldest rock layer first.
Igneous Intrusions: magma injected into older rock layers.
The law of cross-cutting relationships- an igneous rock is younger than the rocks that it has intruded into.
This also applies to faults.
Younger than the rock they are found.
Contact metamorphic rock above and below the intrusion.
Igneous Inclusions: Any included pebbles and fragments embedded in an igneous rock. The inclusions must be older than the host rock containing them.
Igneous Extrusions: formed from lava on the surface of the earth. Younger than the rock layers below.
*Contact metamorphic rock is located on the bottom of the lava flow only.
What is the relative ages of the lettered layers in this drawing?
G, S, H, L, B (there is much more to this story)
The Law of Folds or tilts in rocks are younger than the rocks themselves.
Igneous intrusions and extrusions
Fill in the spaces with the types of intrusions and extrusions.
Unconformity: a buried erosion surface. Formed when an area was uplifted above sea level and eroded. Then later subsided below sea level and new sediments were deposited on top of the eroded surface.
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Depositon
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Uplift, folding/faulting
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Erosion
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Deposition
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Click for a great photo of an unconformity from Thomas McGuire
(your review book author).
Which Letters came first? Test your knowledge.
Don't forget to include Tilting, Faulting and Erosional Unconformities.
Comparing Properties of the rock strata:
Correlation- Matching a layer in one location with a layer formed at the same time in another location.
Correlation Techniques:
Radioactive Dating
What is an absolute age? It is the age of a rock unit, fossil or geologic event expressed in units of time, such as years. A good example is your birthday. You were born at a specific time on a specific day of the year.
It is the actual date at which an event occurred.
How does radioactive decay work?
If an isotope is radioactive, it will break down naturally into a lighter element called a decay product. This process occurs at a predictable rate and can be used to determine how old an object is.
What is a Half-life? A half-life is the time required for half of an element's atoms in a sample to change to the daughter product.
In each half-life only half of the remaining radioactive atoms remain, no matter how large the sample.
YOU CAN SQUISH THE MATERIAL AND EVEN CUT IT INTO HUNDREDS OF PIECES AND THE HALF LIFE WILL STAY THE SAME!
Virtual Dating Extra Credit: The clocks in rocks exercise: become a "Virtual Geochronologist".
Radioactive Isotopes: Found on page one of your reference tables!
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# half-lives
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% Carbon-14
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Absolute Age
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1
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1/2
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5,700 years
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2
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1/4
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11,400 years
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3
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1/8
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17,100 years
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_________
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_________
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Radioactive Dating Interactives:
Questions
1. The graph shows the relationship between mass and time for a radioactive element during radioactive decay. If the rock containing this radioactive material is buried deeper in Earth’s crust and subjected to an increase in temperature and pressure, the rate of radioactive decay will probably
1. decrease
2. increase
3. remain the same
4. decrease, then increase
2. The graph shows the development, growth in population, and extinction of the six major groups of trilobites, labeled A through F. Which inference is best supported by the graph?
1. All trilobites evolved from group A trilobites.
2. The trilobite groups became most abundant during the Devonian Period.
3. Precambrian trilobite fossils are very rare.
4. Trilobites could exist in present-day marine climates.
3. The diagrams show the sequence of events that formed sedimentary rock layers A, B, C, and D. This sequence of events best illustrates the
1. formation of a buried erosional surface (unconformity)
2. movement of rock layers along a fault between layers B and D
3. overturning of rock layers
4. metamorphism of sandstone (layer B) into quartzite
4. In the geologic cross section, the most recently formed rock is at location
1. A
2. E
3. C
4. D
5. Which radioactive element is best suited for determining the age of wooden tools used by prehistoric humans during the last ice age?
1. carbon-14
2. potassium-40
3. uranium-238
4. rubidium-87
6. The age of an igneous intrusion is 50 million years. What is the most probable age of the rock immediately surrounding the intrusion?
1. 10 million years
2. 25 million years
3. 40 million years
4. 60 million years
7. If a radioactive material were cut into pieces, the half-life of each piece would be
1. less than the original specimen’s half-life
2. greater than the original specimen’s half-life
3. the same as the original specimen’s half-life
8. A comparison of the age of Earth, obtained from radioactive dating, and the age of the universe, based on galactic Doppler shifts, suggests that
1. Earth is about the same age as the universe
2. Earth is immeasurably older than the universe
3. Earth was formed after the universe began
4. two dating methods contradict one another
9. The graph shows the decay rates of four radioactive substances, A, B, C, and D. Which radioactive substance shown on the graph below has the longest half-life?
1. A
2. B
3. C
4. D
10. Compared to the length of time for the first half-life of a sample of a radioactive isotope, the length of time for the second half-life is
1. less
2. greater
3. the same
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